HIV is primarily sexually transmitted, and men spread the disease more efficiently than women. HIV is transmitted in semen. In the absence of an effective vaccine and/or curative therapy, HIV control depends on understanding the factors which facilitate its transmission. Strong epidemiological evidence and perhaps the spread, of HIV. This phenomenon has been referred to as "epidemiological synergy". However, the biological basis for epidemiological synergy has not been pursued. In particular, it could be postulated that the ejaculate from infected men contains a higher concentration of HIV. Whereas a variety of methods have been developed to quantitate HIV in blood and plasma, much less work has been done with semen. The proposal is designed i) towards the development and comparison of methods for quantification of HIV in semen; ii) to examine the prevalence of gonorrhea, chlamydia, and trichomonas, in asymptomatic HIV+ men; and iii) to determine whether men with asymptomatic urethral infection shed a greater concentration of HIV than an appropriate control group, and whether STD therapy reduces the shedding of HIV. In the first aim we will develop methods for quantification of HIV-1 in semen, including verification of assays to measure HIV-1 RNA in seminal plasma and correlation with HIV-1 in seminal cells. In aim 2 we will study the dynamics of shedding of HIV in seminal plasma in a cohort of men at different stages of disease; correlate between the concentration of HIV in seminal and blood plasma; and examine the impact of potential cofactors affecting shedding of HIV in semen including mucosal inflammation caused by STDs. In aim 3 we will determine whether treatment of urethritis reduces excretion of HIV-1 in semen. We believe that the goals of this application lend themselves to a better biological understanding of the transmission of HIV. We believe that this information will be important in further development of both behavioral and vaccine HIV prevention strategies.